The Gamecocks (4-4, 2-4 Southeastern Conference) had struggled on offense much of the season and were expected to be a comfortable bounce-back win for the powerhouse Vols (5-3, 2-3) after consecutive defeats to No. 9 Texas A&M and No. 1 Alabama.
Instead, South Carolina's defense bottled up the Vols most of the game, holding them under 300 yards of offense for just the second time this year. Joshua Dobbs threw for only 120 yards and was picked off twice by cornerback Jamarcus King, the final time with 3:50 left in the game and Tennessee needing a dramatic rally.
Tennessee got a final chance with 35 seconds left and drove to the South Carolina 41. But Aaron Medley's desperation, 58 yard field goal attempt was well short on the final play.
"This is a spark," linebacker Bryson Allen-Williams said. "This is the start of something for the next couple of games and next year."
First-year coach Will Muschamp improved to 5-0 all-time against Tennessee, the first four victories coming during his time at Florida.
Bentley was again on target in his second college start at quarterback. He threw for 167 yards and completed 15 of 20 passes, including a 17-yard TD throw to Bryan Edwards and a 35-yard scoring toss to K.C. Crosby in the final period to put South Carolina up 24-14.
Tennessee could not dig itself out of that hole and ended a three-game win streak against South Carolina.
"This is unacceptable," Vols coach Butch Jones said. "Everybody's going to own this and everybody's responsible."
Tennessee: The Vols' third straight SEC loss may have been the most devastating of all as they fall two games behind Eastern Division leader Florida with three league games left. Tennessee will have to root for these same Gamecocks in two weeks when they head to The Swamp to face the Gators.
South Carolina: No question this is Muschamp's biggest victory at South Carolina, and suddenly puts the Gamecocks in line for a bowl game with struggling Missouri and FCS opponent Western Carolina ahead in November.
Count on Tennessee falling from the rankings when it comes out. It's one thing to lose to top-10 opponents, it's another to lose to a team that entered last in SEC scoring offense.
South Carolina lost starting cornerback Chris Lammons and starting safety D.J. Smith to ejections, both for transgressions with Tennessee receiver Jauan Jennings . Lammons threw two punches at Jennings after the two tied up in the opening quarter and he was thrown out for unsportsmanlike conduct. Smith was called for targeting on a hit of Jennings.
Lammons Tweeted later his actions were selfish and he apologized to fans, teammates and coaches.
Tennessee's most explosive play was a 100-yard kickoff return by Evan Berry that cut a 10-point deficit to 17-14 in the third quarter.
Tennessee steps out of conference to play FCS opponent Tennessee Tech at home next Saturday.
South Carolina closes out five straight games at home against Missouri next Saturday.